New storage concepts have been introduced over the past few years profiting from the scanning tunneling microscopy and atomic force microscopy technologies. They exploit the capability of these technologies of imaging and investigating the structure of materials down to the atomic scale. Probes having a tip are being introduced for scanning appropriate storage media, where data are written as sequences of bits represented by indentation marks and non-indentation marks. Such indentation marks may only have a diameter in the range of 30 to 40 nm. Hence, these data storage concepts promise ultra-high storage aereal densities.
A data storage device is disclosed in “The Millipede—more than 1000 tips for future AFM data storage” by P. Vettiger et al., IBM Journal Research Development, volume 44, no. 3, May 2000. The data storage device has a read and write function based on a mechanical x-/y-scanning of a storage medium with an array of probes each having a tip. The probes scan during the operation assigned fields of the storage medium in parallel. In that way high data rates may be achieved. The storage medium comprises a thin polymethylmethacrylate (PMMA) layer. The tips are moved across the surface of the polymer layer in a contact mode. The contact mode is achieved by applying small forces to the probes so that the tips of the probes can touch the surface of the storage medium. For that purpose the probes comprise cantilevers which carry the sharp tips on their end sections. Bits are represented by indentation marks or non-indentation marks in the polymer layer. The cantilevers respond to these topographic changes in the surface while they are moved across the surface.
Indentation marks are formed on the polymer surface by thermomechanical recording. This is achieved by heating a respective probe with a current or voltage pulse during the contact mode in a way that the polymer layer is softened locally where the tip touches the polymer layer. The result is a small indentation in the layer having a nanoscale diameter.
Reading is also accomplished by a thermomechanical concept. The heater cantilever is supplied with an amount of electrical energy, which causes the probe to heat up to a temperature that is not high enough to soften the polymer layer as is necessary for writing. The thermal sensing is based on the fact that the thermal conductance between the probe and the storage medium, especially a substrate of the storage medium, changes when the probe is moving in an indentation as the heat transport is in this case more efficient. As a consequence of this the temperature of the cantilever decreases and hence also its resistance decreases. This change of resistance is then measured and serves as the measuring signal.
However it has been observed, that with an increasing data density on the storage medium the probability of data loss increases. Accordingly, it is a challenge to provide a data storage device and a method for operating a data storage device which enables a high data density and a high reliability.